1. Field of the Invention
The present invention relates to a carrier for use in a two-component developer in an image-forming apparatus such as a digital copying machine or a printer, and more particularly to a binder carrier containing a magnetic particle dispersed in a binder resin.
2. Description of the Prior Art
In a copying machine or printer of electrophotographic system, a two-component developing method using a two-component developer containing a toner and a magnetic carrier is in practical use in developing an electrostatic latent image formed on an electrostatic latent image supporting member such as a photosensitive member.
As a carrier for a two-component developer, various carriers are known such as an iron particle carrier, a ferrite carrier, a resin-coated carrier containing these magnetic particles coated with a resin, a binder carrier containing magnetic fine particles dispersed in a binder resin. However, resin-coated carriers raise a problem that a smooth image cannot be obtained due to their hard ear when they are transported as a magnetic brush on a developing roller or problems such as disturbance of toner images or damage to the photosensitive member due to scraping. Also, the resin-coated carrier has a problem that its life as a developer is short due to peeling-off of the coating layer during its use.
The binder carrier can solve the above-mentioned problems, and is further attracting public attention as a carrier which can be produced easily in small particles, which has a high volume specific electric resistance, and into which electric charge from a developer-supporting member is not easily transferred.
However, conventional binder carriers raise a problem that the toner itself, a charge-controlling agent of the toner, a post-processing agent, or the like adhere to the carrier surface during their use, whereby the charging efficiency of the carriers deteriorates to provide insufficient charging with the toner, resulting in a toner flying phenomenon or an image noise such as fogging in an image formed on a sheet. This problem becomes conspicuous in a full color developing process that uses a large amount of toner.